This invention relates to power shovels and more specifically to a power shovel having an improved front end assembly. This invention particularly is applicable to large, heavy-duty mining shovels of the type disclosed in U.S. Pat. Nos. 3,501,034; 3,648,863 and 3,990,161.
In conventional, heavy-duty mining shovels, usually there is provided a lower frame provided with a propulsion unit, a rotatable upper frame mounted on the lower frame, a stiffleg operatively connected to the upper frame, a handle operatively connected to the stiffleg, a dipper mounted on the handle, a system for crowding the dipper and a system for hoisting the dipper. Typically, the hoist system of such type of shovel consists of a rope assembly, generally including a hoist drum mounted on the upper frame, driven by motor-generator sets through heavy-duty gear trains, sheaves mounted on the front end assembly of the machine and a rope wound on the hoist drum, reeved on the sheaves and dead-ended at the foot of the stiffleg. By paying out and taking in the hoist rope, the handle can be pivoted relative to the stiffleg to hoist and lower the dipper.
Hoist systems of the type described have several disadvantages. Initially, there are the original and replacement costs of the motor-generator sets, the heavy-duty gearing, the hoist drum, the sheaves and the ropes, which are substantial. Secondly, there is the disadvantage of the requirement for space of the hoist system components mounted on the upper frame. The motor-generator sets, gearing and hoist drum normally are mounted on the upper deck of the machine which usually is congested with other components of the machine including structural components of the housing and operator's cab, the crowd machinery, the swing machinery, the propulsion machinery and various auxiliary systems and equipment. Rope wear and fouling also are disadvantages of rope hoist systems which result in increased downtime for repair and maintenance. It thus has been found to be desirable to provide an improved front end assembly for power shovels, particularly for large, heavy-duty mining shovels, and specifically to provide an improved hoist system which would mitigate if not entirely eliminate the aforementioned disadvantages of rope systems.
In the normal operation of machines of the type described, in addition to normal tensile, compressive and bending loads being applied to the dipper which oridinarily are transmitted through the dipper, handle and stiffleg to the main frame of the machine, side loads are applied to the dipper and transmitted to the main frame of the machine which can be substantially detrimental to the machine. To counteract the detrimental effects of such side loads, it has been a practice in the prior art to utilize resilient joints in the handle or stiffleg which function to cushion such loads and to prevent the loads from being transmitted to the main frame of the machine. While being beneficial in cushioning side loads, such joints have certain disadvantages such as added cost and increased weight on the front end of the machine which increases horse power requirements and reduces the operating efficiency of the machine.